1. Field of the Invention
The present invention relates to a pulse signal receiving apparatus and a transmission system.
Priority is claimed on Japanese Patent Application No. 2010-274949, filed Dec. 9, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
As is well known, digital signal transmission schemes may be divided broadly into a baseband scheme and a broadband scheme. The baseband scheme is a transmission scheme in which a digital signal is directly transmitted without being modulated. The broadband scheme is a transmission scheme in which a digital signal is modulated into an analog signal and the analog signal is transmitted. Representative transmission schemes for use in the broadband scheme may be a pulse width modulation (PWM) scheme, a pulse amplitude modulation (PAM) scheme, a pulse position modulation (PPM) scheme, and the like.
In the related art, the PWM or PPM scheme is usually used in the field of power control or motor control. However, in recent years, the PWM or PPM scheme has also been used in infrared communication by an infrared data association (IrDa) standard, high-speed optical communication, and high-speed wireless communication of ultra wide band (UWB), because reduction of power consumption is possible and speeding up is facilitated.
The PWM scheme is classified as either a single-edge modulation scheme or a double-edge modulation scheme. The single-edge modulation scheme is a modulation scheme in which either a period in which a pulse signal has a “high (H)” level or a period in which the pulse signal has a “low (L)” level is modulated. The double modulation scheme is a modulation scheme in which both the period in which the pulse signal has the “H” level and the period in which the pulse signal has the “L” level are modulated. If the double-edge modulation scheme is used, it is possible to implement higher performance (in terms of transmission rate, control responsiveness, or the like) as compared to when the single-edge modulation scheme is used. A difference between a pulse signal modulated by the single-edge scheme and a pulse signal modulated by the double-edge scheme is disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. H9-84388.
In the pulse signal modulated by the double-edge modulation scheme, a pulse edge defines an end time of a certain period (for example, a period of the “H” level) and a start time of a period following the period (for example, a period of the “L” level). Thus, if a position of the pulse edge fluctuates due to noise or the like, a deviation (error) occurs in both periods before and after the pulse edge and a transmission error occurs. In addition, if the position of the pulse edge continuously fluctuates, the transmission error increases due to an accumulated deviation.
Although it is possible to remove noise of a low frequency component and a high frequency component if a band pass filter (BPF) is used, it is not possible to remove noise of the same frequency band as a frequency band of a pulse signal modulated by the double-edge modulation scheme. Thus, it is not possible to suppress the position fluctuation of the pulse edge due to noise even when the BPF is used. Although an influence of the position fluctuation of the pulse edge may be reduced if a degree of modulation is set with a margin considering the influence of noise, it is difficult to implement a high transmission rate.